The Federal Trade Commission (FTC) defines and enforces "Made in USA" claims. Their definition is based on a product being made (and sourced) "all or virtually all" in the USA.

From the FTC, "All or virtually all" means that all significant parts and processing that go into the product must be of U.S. origin. That is, the product should contain no — or negligible — foreign content."

There is some ambiguity in the standard. For example, a lighting fixture with US-made body and stake but foreign-made lens and socket might or might not comply. The standard considers place of final assembly (must be USA), the importance of the foreign-made part(s) to the functionality of the final product, and the relative monetary value of the foreign part(s).

The recent adoption of LED's does call into question some "Made in USA" claims since mfgs. are claiming LED's as a prime feature of the product and LED's are expensive. If these LED's and their drivers come from Asia (as most do) then it's hard to claim that they are a negligable part of the product.

The other source to consider is the "Buy America Act". Passed in 1933, it mandates that US-made products be selecting for Government contracts. It is also an important part of Obama's American Recovery and Reinvestment Act and for the DOE's Leadership in Energy and Environmental Design (LEED) program.

The "Made in USA" qualifications for these programs and government contracts are much more flexible than the FTC standards, and include exclusions relevent to the project at hand, and allow products made in countries that participate in free trade agreements.

This is why most CAST products can not claim "Made in USA" on the packaging (since they're made in Colombia), but they do qualify for BUY American (hence LEED credits) since the USA has a free trade agreement with Colombia.